Sucrose is the main product of photosynthesis in plants, providing a rich carbon and energy source for the physiological growth and development of insects. In a previous study, we identified a novel sucrose hydrolase (SUH) in the larval midgut of moths. Intriguingly, there are two copies of Suh, namely Suh1 and Suh2, in several species of butterflies. However, the biochemical characteristics of SUHs in butterflies remain unclear. In this study, we found that this duplication and subsequent diversification produced two Suh genes in Papilio xuthus. These two PxSuh genes were significantly divergent in terms of their expression pattern and enzyme properties. PxSuh messenger RNA expression was highest during the larval stage, reduced in the prepupal and pupal stages and, for PxSuh1, slightly increased again in the adult. The observed levels of PxSuh2 were overall below those of PxSuh1 amongst the development stages examined. Compared with PxSUH2, which has maintained the original gene function of maltose hydrolysis, PxSUH1 exhibits substrate specificity for sucrose with an optimum enzyme activity occurring at an alkaline pH. The data show that PxSuh1 is evolutionarily adapted for effective functioning in an alkaline digestive system. Furthermore, we find that functional diversification of Suh facilitates P. xuthus to digestive carbohydrate of host plants. Thus, our findings offer new insights into the ecological and evolutionary adaptation of digestive enzymes in butterflies.

中文翻译：

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Papilio xuthus中蔗糖水解酶的基因复制和随后的功能多样化。

蔗糖是植物光合作用的主要产物，为昆虫的生理生长和发育提供了丰富的碳和能源。在以前的研究中，我们在蛾的幼虫中肠中发现了一种新型的蔗糖水解酶（SUH）。有趣的是，在几种蝴蝶中都有Suh的两个副本，即Suh1和Suh2。然而，SUHs在蝴蝶中的生化特征仍不清楚。在这项研究中，我们发现这种重复和随后的多样化在xapius中产生了两个Suh基因。这两个PxSuh基因在表达方式和酶学性质上均存在明显差异。PxSuh在幼虫期，信使RNA的表达最高，在pu前和p期降低，而对于PxSuh1，成年后的信使RNA的表达又略有增加。所观察到的水平PxSuh2是整体低于那些PxSuh1当中检查了发展阶段。与保持麦芽糖水解的原始基因功能的PxSUH2相比，PxSUH1对蔗糖表现出底物特异性，并在碱性pH值下具有最佳的酶活性。数据表明，PxSuh1经过进化适应于碱性消化系统中的有效功能。此外，我们发现Suh的功能多样化促进了P. xuthus吸收宿主植物的消化碳水化合物。因此，我们的发现为蝴蝶消化酶的生态和进化适应提供了新的见解。